The invention generally relates to a perforating gun.
For purposes of enhancing production from a subterranean formation, a perforating gun typically is lowered down into a wellbore (that extends through the formation), and radially oriented shaped charges (of the perforating gun) are detonated to form perforations in the formation. The shaped charges typically are placed at points along a helical spiral that extends around a longitudinal axis of the perforating gun. The angular displacement (with respect to the longitudinal axis) between the adjacent charges along this path defines a phasing of the gun. Typically, specified parameters, such as a shot density and the phasing, control the number of shaped charges of the gun, the angular positions of the shaped charges and the distances along the longitudinal axis between the shaped charges.
For example, FIG. 1 depicts a carrier tube-type perforating gun 10 that includes shaped charges 14 (charges 14a, 14b and 14c depicted as examples) that are alternatively phased (relative to each other) at 0xc2x0 and 180xc2x0 about the longitudinal axis of the gun 10, i.e., the shaped charges are phased 180xc2x0 apart. In this manner, the top charge 14a of the perforating gun 10 in FIG. 1 is positioned at 0xc2x0 (as a reference point), the middle charge 14b is positioned at 180xc2x0 and the bottom charge 14c is positioned at 0xc2x0. Thus, each adjacent pair of charges 14 is phased differently (at 0xc2x0 and 180xc2x0). The charges 14 are housed inside a hollow carrier tubing 11, and a detonating cord 12 extends between and is connected to the charges 14 to communicate a detonating wave to the charges 14. Although a carrier tube-type perforating gun is depicted in FIG. 1, another structure may hold and orient the charges 14, such as a strip (in a strip-type perforating gun) to which the ends of the charges 14 are connected.
A distance (called xe2x80x9cdxe2x80x9d in FIG. 1) between adjacent charges 14 governs the shot density of the perforating gun 10. Thus, to increase the shot density of the perforating gun 10, the distance d is decreased, and to decrease the shot density of the gun 10, the distance d is increased. However, factors limit the maximum shot density of the gun 10. For example, the closer the adjacent charges 14 are together (i.e., the smaller the distance d), the more the detonating cord 12 bends between the charges 14, a factor that increases a cord-to-charge interference between the detonating cord 12 and the charges 14. Furthermore, if there is interference between the charges 14, the closer the adjacent charges 14, the greater the charge-to-charge interference between the charges 14. In this manner, charges 14 that have opposite phases typically significantly interfere with each other when the charges 14 are placed too close together.
Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are stated above.
In one embodiment, a technique includes arranging perforating charges of a perforating gun into groups of adjacent perforating charges. Each perforating charge of each group is aligned in a single direction associated with the group. The groups are oriented to form a phasing for the perforating gun.
Other embodiments and features will become apparent from the following description, from the drawings, and from the claims.